Estradiol valerate (INN, USAN; brand names Altadiol, Deladiol, Delestrogen, Estraval, Progynova, Valergen, many others), or oestradiol valerate (BAN), is a synthetic ester, specifically the 17-pentanoyl ester, of the natural estrogen, 17β-estradiol.[2][3] It was introduced in the 1950s, and along with estradiol benzoate and estradiol cypionate, has since become one of the most widely used esters of estradiol.[4] Upon ingestion, regardless of the route of administration, estradiol valerate behaves as a prodrug, being cleaved by esterases in blood plasma and the liver into 17β-estradiol and valeric acid.[5][6] However, compared to estradiol itself, estradiol valerate is absorbed more slowly and possesses a longer duration, especially when given in an oil solution via intramuscular injection (in which it acts as a depot), and as a result, can be administered less frequently.[7][8]